1. Field of the Invention
The present invention relates to an electromagnetic actuator that generates a driving force by an electromagnetic force. More specifically, the present invention relates to an electromagnetic actuator that includes a rotor having a magnetized outer peripheral surface and a yoke that forms a magnetic-pole part facing the outer peripheral surface of the rotor and that is used when a blade member of a camera, such as a shutter blade or a diaphragm blade, is driven, and relates to a camera blade driving device using the electromagnetic actuator.
2. Description of the Related Art
A conventionally known electromagnetic actuator mounted on, for example, a shutter device of a camera includes a cylindrical rotor that is supported rotatably with respect to a base plate having an exposure aperture and that is magnetized into N and S-poles by bisecting its outer peripheral surface in the circumferential direction, a nearly U-shaped yoke that has a magnetic-pole part disposed to face the outer peripheral surface of the rotor, and a magnetizing coil wound around the yoke (see Japanese Unexamined Patent Publication Nos. H9-152645 and 2001-327143, for example).
An other conventionally known electromagnetic actuator includes a cylindrical rotor that is supported rotatably with respect to a base plate having an exposure aperture and that is magnetized into N- and S-poles by bisecting its outer peripheral surface in the circumferential direction and a protrusion part that is protruded in the circumferential direction with respect to the rotor, in which the protrusion part is fixed so as to be rotatable together with the rotor and in which the rotational range of the rotor is restricted by bringing the protrusion part into contact with a stopper formed on the base plate (see Japanese Unexamined Patent Publication No. H7-13215, for example).
Meanwhile, correspondingly to a reduction in size of, for example, a digital camera, an electromagnetic actuator mounted on the digital camera is required to be reduced in size. If the electromagnetic actuator is merely reduced in size without changing the conventional structure, the magnetized cylindrical rotor becomes small in size, and it becomes difficult to sufficiently secure a driving torque generated by the rotor during energization and a magnetic attraction force generated during non-energization. Accordingly, when the electromagnetic actuator is used as a driving source that drives a shutter blade, etc., it becomes difficult to stably drive the shutter blade and hold this at a predetermined position.